World-wide synthetic fiber production has expanded greatly in recent years and today millions of pounds of synthetic fibers are manufactured annually. A substantial and increasing portion of such production consists of polyester fibers. Such polyester fibers are frequently manufactured from terephthalic acid and ethylene glycol.
In the manufacture of fabrics and wearing apparel from terephthalic acid-ethylene glycol type polyester fibers large quantities of scrap and cuttings are produced. In fact, there are believed to be several hundred million pounds of such scrap produced annually. Heretofore such scrap has either been destroyed or sold as scrap for various secondary or incidental uses. The destruction of such scrap, as for example, by incinerating or dumping, has contributed to the world's environmental problems.
Final products other than fibers are also manufactured from polyester polymers and in such production large quantities of scrap are also generated. And, as in the case of the fabric scrap, there exists the problem of disposal and a need for recovering for reuse the components of the polyester material.
In addition to the need to reduce environmental contamination there also exists a need for terephthalic acid and ethylene glycol. In fact, with the increasing demand for such materials and the reduced supplies of feedstocks to produce them, there is a current shortage of them.
In U.S. Pat. No. 3,317,519 there is disclosed a process, primarily directed to recovering caprolactam from processes polyamidepolyester fabric, where terephthalic acid is also recovered. Other porcesses for recovering terephthalic acid from other materials are also described in the following U.S. Pat. Nos. 3,098,046, 3,108,082, 3,120,561, 3,222,299, 3,488,299, and 3,594,414.
Even though there has existed a need in the art to recover terephthalic acid from polyester materials, no one has devised a process which will do so without the need to use exotic chemicals, elevated temperatures, high pressures and/or expensive equipment. Moreover, no process is known whereby the recovery is achieved quickly and with terephthalic acid yields approaching 100% of theoretical maximum yield. This invention is, therefore, directed to providing such a process.
An important objective of this invention is to recover terephthalic acid from polyester materials without the use of elevated temperatures and pressures. Another important objective has been to provide such a process that economically recovers terephthalic acid. A still further objective is to recover not only terephthalic acid from a terephthalic acid-ethylene glycol polyester, but to recover the ethylene glycol as well. And, lastly, a principal objective has been to provide an ecologically "clean" process for recovering the terephthalic acid.